Both "contact" and "contactless" smart cards are known per se. Generally, such smart cards are provided either with electrical contacts for effecting direct electrical contact with a card reader; or else they are provided with an antenna coil for effecting contactless bi-directional communication with a remote card reader. U.S. Pat. No. 5,206,495 for a Chip Card in the name of H. D. Kreft discloses a chip card allowing both contact and contactless communication in a single smart card.
Contactless smart cards are particularly suited for applications, such as mass transport systems, wherein data communication must be effected very quickly without imposing the overhead incurred in manually introducing the smart card into the slot of a card reader.
U.S. Pat. No. 5,206,495 has as a principal object thereof the provision of a contact/contactless chip card having a semiconductor device selectively coupled either to a contact field or to a antenna coil. A further declared feature is that the semiconductor device operates according to contact mode protocol (ISO Standard 7816) regardless of the mode of data transfer, such that the semiconductor device perceives no difference between contact and contact-free use of the chip card.
Such chip cards employ an on-board semiconductor device including memory and processing capability for effecting the desired bi-directional data transmission and data storage. In the case where "contact" data transmission is required, there is provided a so-called "contact field" having a plurality of contacts, each of which is selectably connected to the semiconductor device by means of a respective electrical connection. Data transmission with an external reader is then effected by inserting the card into a suitable reader having spring-loaded contacts which bear on respective contacts in the contact field of the chip card.
Alternatively, when contactless data transmission is required, a pair of antenna coils in the chip card are adapted to transfer power to the card and to enable bi-directional data communication with a reading device having a similar antenna.
The interconnection provided by U.S. Pat. No. 5,206,495 allows for a semiconductor device conforming to ISO Standard 7816 for "contact" bi-directional data transmission also to be used for "contactless" type data transmission without in any way modifying the semiconductor device. On the other hand, such an approach exacts a price in the efficiency of data transfer owing to the inherent differences between efficient contactless data protocols and the ISO 7816 contact protocol, which thus requires that the card include a data conversion facility if the semiconductor device is to perceive the same protocol in both contact and contactless modes. The use of two coils is also considered a retrograde step reminiscent of the early U.S. Pat. No. 3,299,424 (Vinding) wherein multiple coils were employed: a trend which has long been abandoned in favor of the use of a single coil only.
International Patent Publication No. WO 96/38814 (Mikron) discloses an arrangement functionally similar to that shown in U.S. Pat. No. 5,206,495 in that contact and contactless data and control lines are switchably connected to a processing unit shown as 13d. To this end there are provided separate CLOCK, DATA and RESET lines in both the contactless and contact interfaces 13b and 13c, respectively, which are connected via a switching element shown as 13a.
Yet a further consideration associated with the increasing use of smart cards is the need to customize each smart card for the particular application for which it is destined. Obviously, the provision of both contact and contactless modes of data transfer increases the card's versatility since the actual mode of data transfer may then be selected according to user requirements. However, in practice, there are many other features associated with smart cards which also must be optimized for each specific application, be it contactless access control or mass transportation or contact mode bank applications and so on.
Such versatility is addressed by our co-pending WO 98/29830 filed on Dec. 29, 1997 which discloses a data transaction card having contact and contactless modes of operation, comprising a semiconductor device for operating in contact and contactless modes in accordance with a respective contact or contactless data communications protocol. A contact field includes contacts fixedly connected to the semiconductor device for allowing data transmission between the contacts and the semiconductor device in accordance with the contact data communications protocol, whilst an antenna coil allows contactless data transmission between the antenna coil and the semiconductor device, in accordance with the contactless data communications protocol. An antenna interface is coupled to the antenna coil, to the semiconductor device and to at least some of the contacts in the contact field and is responsive to an electromagnetic field across the antenna coil for effecting the contactless data transmission.
Preferably, in such an arrangement, the contactless data communications protocol is in accordance with ISO 14443 which also sets a low amplitude modulation for data transmission both from the reader to the card as well as from the card to the reader. This modulation limit is designed to prevent the amplitude of the high frequency carrier falling to a level which could cause interruption of the energy transfer via the modulated carrier wave between the reader and the card which has no separate energy source of its own. It also reduces sidebands and therefore allows a relative increase in the intensity, or signal strength, of the fundamental center frequency, thereby increasing the operating range of the application. ISO 14443 also caters for 100% amplitude modulation when transmitting data from the reader to the card. The resultant interruption of energy transfer to the card must be allowed for.
U.S. Pat. No. 5,241,160 assigned to the present applicants discloses a bi-directional contactless data transaction card wherein the reader has a matched antenna circuit allowing the tuned frequency thereof to be maintained regardless of any changes in the length of cable connecting the antenna thereto. According to a preferred data communications protocol, data is transferred from the reader to the card by using a specially adapted 100% amplitude modulation, pulse width encoded signal, responsive to data bits of a defined logic level. As a result, energy transfer to the card is momentarily interrupted. During, this brief time interval, the logic functions of the card are sustained via a capacitor which is charged during the period of time that energy is transferred from the reader to the card. Data is transferred from the card to the reader by decoupling, the tuned antenna circuit in the card. Such a decoupling technique results in a significant increase in the signal level of the reader antenna than is achieved by any other loading scheme. It also causes interruption of power transfer to the card via the carrier signal, during which power is maintained via the capacitor. These advantages notwithstanding, decoupling the card antenna does not conform to the prevalent ISO 14443 standard.
There are clearly advantages to be gained in providing a data transaction card which allows for carrier wave modulation to be performed both according to ISO 14443 as well as to our own proprietary protocol. This would allow more efficient manufacture with reduced stocks resulting in a single card offering upward compatibility for existing users whilst also supporting the ISO 14443 protocol.
It would therefore be a significant improvement if there were provided a data transaction card having a contactless interface allowing low or 100% amplitude modulation of the reader carrier signal for reader to card data transfer and also allowing for either decoupling or partial loading of the tuned antenna circuit therein for card to reader data transfer, so as to allow for compatibility with all applications and also to offer greater versatility to those end users who will thus be free to choose whichever protocol better suits their needs.